The present invention relates generally to safety belt restraint systems for motor vehicles and, more particularly, to an end release seat belt buckle equipped with an inertia-sensitive locking mechanism for inhibiting release of the tongue plate from latched engagement with the seat belt buckle when the vehicle is subjected to a deceleration force exceeding a predetermined value.
Modernly, virtually all motor vehicles are equipped with some type of passenger restraint system for physically restraining the seat occupant when the vehicle is subjected to high rates of deceleration which may occur, for example, during heaving braking or collision. As is known, the most common type of passenger restraint system is a seat belt system having at least one of a lap belt and a shoulder belt, or combination thereof, that can be withdrawn from a retractor device for latched engagement of a tongue plate with an anchored belt buckle. One type of retractor, commonly referred to as an "Emergency Locking Retractor" (ELR), is operable to permit the seat belt to be freely withdrawn from the retractor in response to movement of the seat occupant during normal vehicular operating circumstances, thereby providing increased comfort and freedom of movement for the seat occupant. In this mode of operation, the retractor exerts a retractive tensioning force on the seat belt for tightening it against the seat occupant. Moreover, emergency locking retractors also include a locking mechanism for inhibiting withdrawal of the seat belt when the vehicle is subjected to a deceleration force exceeding a predetermined critical value, thereby restraining the vehicle occupant. In many instances, the locking mechanism is "inertia-sensitive" and is actuated in response to the deceleration force being exerted thereon.
In addition, many retractors are also equipped with a tension release device or so-called "comfort" mechanism that can be selectively actuated to prevent the retractor from exerting the above-noted tensioning force on the seat belt which may be uncomfortable and annoying to some seat occupants. However, the "slack" generated by the comfort mechanism can thereafter be cancelled by withdrawing a relatively short length of the seat belt from the retractor. An example of such a seat belt retractor is shown and disclosed in commonly owned U.S. Pat. No. 5,121,887 entitled "Comfort Mechanism For Seat Belt Retractor Assembly".
It is known that the existence of "slack" in the seat belt may permit the seat occupant to be thrown forward and collide with on-board structures when the vehicle is subjected to a large deceleration force. To prevent such collisions, the protection afforded by conventional seat belt systems can be further enhanced by the use of a belt tensioning mechanism. In general, a belt tensioning mechanism functions, in conjunction with lock-up of the retractor, to remove slack from the seat belt immediately upon detection of the deceleration force. As such, forward excursions of the seat occupant are significantly minimized. In some restraint systems, the belt tensioning mechanism is coupled to the belt buckle for causing retractive movement thereof so as to remove slack and exert a tensioning load on the seat occupant. As will be appreciated, the belt tensioning mechanism must be equipped with a large pre-loaded drive arrangement (i.e., pre-loaded spring, pyrotechnic device, etc.) that can be automatically triggered for retracting the belt buckle in response to detection of the vehicular deceleration condition. Examples of mechanically-actuated and electronically-actuated "buckle-type" belt tensioning mechanisms are respectively shown in commonly owned U.S. Pat. Nos. 5,211,423 and 5,364,129.
While the incorporation of a buckle-type belt tensioning mechanism into vehicular safety belt restraint systems is a highly desirable feature, various design considerations regarding the remainder of the system must be addressed. In particular, the belt buckle must be capable of maintaining latched engagement with the tongue plate during its retractive movement despite the extremely high acceleration loading (i.e., greater than 200 g's) exerted on the belt buckle upon activation of the belt tensioning mechanism. This concern is particularly applicable to "end release" type belt buckles which have a spring-biased release button that is longitudinally movable in a direction substantially parallel to the direction of the retractive movement of the belt buckle. The release button is normally biased toward a latched position and, under normal vehicular conditions, must be forcibly moved to an unlatched position in opposition to the biasing for releasing the tongue plate from latched engagement with the belt buckle. However, when the buckle-type belt tensioning mechanism is activated and the belt buckle is completely retracted, the inertia acting on the release button may overcome the biasing and forcibly move the release button to its unlatched position.
In view of the foregoing, the need exists to provide an end release belt buckle having means for inhibiting unintentional release of the tongue plate during a vehicular deceleration and yet which can be easily manufactured and assembled.